pale lavender galaxy
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by
p.draper
Is this a true colour ? P Draper
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by
JeanTate
in response to p.draper's comment.
No, not even close.
On a clear, dark, moonless night, a long way away from any city (or other) lights, if you look up you may see the Milky Way, our own galaxy, as a ribbon of faint light (with splotches, both bright and dark). Because it's so faint, it doesn't really have a color. And it won't have a color if you look at it through a telescope, no matter how big or how great the magnification. Why? Because the light is spread out, it's 'surface brightness', and surface brightness doesn't change.
(There are, very likely, some parts of some galaxies which have have a high enough surface brightness to trigger the cones in your eyes; however, for the most part these would appear as slightly bluish or yellowish white)
The SDSS images we are served up, here in Galaxy Zoo, are highly processed from the digital data that comes from the camera; in particular, the processing algorithm greatly exaggerates the hue, and cranks the saturation way up. Also, the three camera filters ('bands') that are mapped to the RGB of the JPEG images are not anything like 'red', 'green', or 'blue': R is the 'i' band, which is in the infrared (so our eyes can't see this light at all); G is the 'r' band, which we'd see as (deep) red; B is the 'g' band which we'd see as yellowish green (depends on what the source is).
There is one kind of galaxy which does have a color, the Green Peas zooites discovered. Many of these have high surface brightness and almost all the visible light comes from just a few emission lines.
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